DESCRIPTION: The goal of this research project is to use the functional imaging technique, PET, to determine if a reduction in the functional activity of cholinergic neurons is associated with age-related deterioration in cognitive function. The study will compare PET-derived indices of cholinergic function in elderly monkeys who have memory and learning deficits with similar results in unimpaired young and elderly monkeys. The specific aims of the project include: (1) to identify patterns of individual variations in the severity of cognitive deficits observed in aged rhesus monkeys; (2) to measure baseline cholinergic activity using PET derived quantitation of F-18 FBT concentrations in the striatum of functionally impaired and unimpaired monkeys; (3) to measure the functional responsivity of the cholinergic system in response to D-2 blockade in functionally impaired and unimpaired monkeys; and (4) to measure the differences in dopamine D-2 receptor binding potential in these same populations of monkeys with F-18 labeled FCP. The PET derived indices of cholinergic function will be correlated with levels of functional impairment in the young and elderly monkeys.